feat: Enhance PostgreSQL type handling and migration scripts

- Introduced equivalent base types and variants for PostgreSQL types to normalize type comparisons.
- Added functions for normalizing SQL types and retrieving equivalent type variants.
- Updated migration writer to handle type alterations with checks for existing types.
- Implemented logic to create necessary extensions (e.g., pg_trgm) based on schema requirements.
- Enhanced tests to cover new functionality for type normalization and migration handling.
- Improved handling of GIN indexes to use appropriate operator classes based on column types.

cmd/relspec/merge_from_list_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -160,3 +161,38 @@ func TestRunMerge_FromListMissingSourceType(t *testing.T) {
 		t.Error("expected error when neither --source-path nor --from-list is provided")
 	}
 }
+
+func TestRunMerge_PgsqlOutputRejectsColumnTypeConflict(t *testing.T) {
+	saved := saveMergeState()
+	defer restoreMergeState(saved)
+
+	dir := t.TempDir()
+	targetFile := filepath.Join(dir, "target.json")
+	sourceFile := filepath.Join(dir, "source.json")
+	writeTestJSONWithSingleColumnType(t, targetFile, "users", "integer")
+	writeTestJSONWithSingleColumnType(t, sourceFile, "users", "uuid")
+
+	mergeTargetType = "json"
+	mergeTargetPath = targetFile
+	mergeTargetConn = ""
+	mergeSourceType = "json"
+	mergeSourcePath = sourceFile
+	mergeSourceConn = ""
+	mergeFromList = nil
+	mergeOutputType = "pgsql"
+	mergeOutputPath = ""
+	mergeOutputConn = "postgres://relspec:secret@localhost/testdb"
+	mergeSkipTables = ""
+	mergeReportPath = ""
+
+	err := runMerge(nil, nil)
+	if err == nil {
+		t.Fatal("expected pgsql output merge to fail on column type conflict")
+	}
+	if !strings.Contains(err.Error(), "column type conflicts detected") {
+		t.Fatalf("expected conflict summary in error, got: %v", err)
+	}
+	if !strings.Contains(err.Error(), "public.users.id") {
+		t.Fatalf("expected conflicting column path in error, got: %v", err)
+	}
+}